1. Field of the Invention
The invention relates to a process for cutting coked metal molded parts.
2. Discussion of the Background
In large-scale factories, in which hydrocarbons are exposed to high temperatures, these hydrocarbons decompose and form coke deposits on the inside walls of the system in which they are used. This particularly holds true for thermal cracking processes in mineral oil processing or petrochemistry, e.g. olefin systems. For example, it is necessary in such olefin systems to decoke the cracking pipes in the ovens. The coke deposits can reach significant thicknesses, up to complete clogging of the pipes. So-called brittle cracking can occur in cracking pipes that are not decoked, after an operating period of about three years. The same holds true if emergency shut-down of the ovens took place. Increased stresses at the pipe wall occur because of the volume increase which results from the formation of carbonized zones inside the pipes. Intergranular stresses result from structural changes. The coke deposits also result in increased stresses in the pipe wall, due to a difference in shrinkage between the coke and the metal. Because of the coke deposits that remain in the cracking pipes, significant tensile stresses occur during cooling, because the coke deposits have a significantly smaller heat expansion coefficient than the metal material. Cutting the metal by usual cutting methods, such as cutting wheels or air saws, is not possible without danger, since the pipes can burst and pieces of pipe can fall unchecked into the oven space. Water cutting can also be used only with restrictions, and requires additional complicated measures for protecting workers. Breaking the coked molded parts out using hydraulic presses is not a suitable method, due to the fact that it could bring about secondary damage, for example, to the surrounding walls.